Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a first image in a sequence for a display screen or portion thereof with transitional graphical user interface showing our new design;

FIG. 2 is a second image thereof;

FIG. 3 is a third image thereof;

FIG. 4 is a fourth image thereof;

FIG. 5 is a fifth image thereof; and,

FIG. 6 is a sixth image thereof.

The appearance of the animated user interface sequentially transitions between the images shown in FIGS. 1-6. The process or period in which one image transitions to another forms no part of the claimed design. The broken line showing of the alphanumeric characters, symbols, graphic elements and the display screen or portion thereof forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with transitional graphical user interface, as shown and described. 